The subject invention discloses new and useful phenyloxazolidinone compounds having a nitrogen containing hetero-aromatic ring substitution attached through one of the nitrogen atoms. More particularly a 5-member nitrogen containing aromatic ring having from 1 to 4 nitrogen atoms one of which binds to the phenyloxazolidinone. The compounds are useful antimicrobial agents, effective against a number of human and veterinary pathogens, including gram-positive aerobic bacteria such as multiply-resistant staphylococci, streptococci and enterococci as well as anaerobic organisms such as Bacteroides spp. and Clostridia spp. species, and acid-fast organisms such as Mycobacterium tuberculosis, Mycobacterium avium and Mycobacterium spp..